Murine typhus is unique among the major arthropod-borne infections in that[unreadable] it can be a household infection because of its intimate association with[unreadable] commensal animals and their fleas. Existing knowledge does not adequately[unreadable] explain many important features and mechanisms which are involved in the[unreadable] extraordinarily successful spread, establishment and maintenance of this[unreadable] zoonosis. This research proposal will examine, under controlled conditions[unreadable] in the laboratory, using quantitative techniques, selected components and[unreadable] interactions of the rickettsia-vector complex. The project goals are: (1)[unreadable] Molecular characterization of ELB to understand its taxonomic and[unreadable] biological relationships with the members of the typhus group and in[unreadable] particular, Rickettsia typhi. Studies include sequencing of 16s rDNA and[unreadable] PCR/RFLP analysis of selected samples of R. typhi and ELB isolates[unreadable] obtained from opossums and humans. Also included under this specific aim[unreadable] are the isolation of ELB agent from the infected human and opossum blood[unreadable] specimens, establishing ELB infection in cultured mammalian cell lines,[unreadable] laboratory rats, and experimental infection of the cat flea,[unreadable] Ctenocephalides felis; (2) To determine the degree of interplay between[unreadable] the R. typhi and ELB agent in arthropod vectors and mammalian hosts. In[unreadable] particular, the following studies will be carried out: (A) dynamics of[unreadable] rickettsial infection in the flea midgut epithelial cells, (B) association[unreadable] of cytoplasmic incompatibility in fleas due to germ line infection with R.[unreadable] typhi and ELB, and (G) identification of rickettsial proteins that may be[unreadable] expressed or underexpressed during the rickettsial transition between[unreadable] fleas and mammalian hosts; and (3) Identification, cloning and[unreadable] characterization of the genes encoding R. typhi and ELB 120 kDa surface[unreadable] protein antigens (SPAs). Rickettsial SPAs are the most abundant surface[unreadable] proteins, and have been of interest because of their strong immunogenecity[unreadable] and species-specific antigenic properties. Therefore, limited[unreadable] immunological studies will be performed to determine the degree of cross[unreadable] protection in animals immunized with P. typhi and ELB upon challenge with[unreadable] the heterologous rickettsiae and involvement of 120 kDa in the protection.[unreadable] [unreadable]